You and Your Students
Vicki Cobb, Education World Science Editor
See how freezing temperatures affect bubbles.
Physical Science, Weather
Setting the Scene (Background)
This experiment is only for those of you who live where it gets very cold -- 10 degrees or below -- in winter. I know that it's much more pleasant to stay inside when the weather gets frigid, but you can take advantage of nature's freezer to show your kids something amazing and fun. Besides, there's nothing like having something interesting to think about to get your mind off the cold. As a hard-core skier, I know.
Bundle up your kids and take them outside. This activity only takes a few minutes, which will not be too difficult to endure. Before you go out, however, ask your students if they know what happens to water when the temperature drops. Do they know the freezing point of water? If not, they are going to see a dramatic example.
You might think that blowing bubbles is a summertime activity. It is -- but it can be a whole new experience in the dead of winter. Wait for an exceptionally cold day: 10 degrees Fahrenheit (-12 degrees Celsius) or below. Create bubbles with an ordinary bubble solution and a wand. Try drawing the wand through the air. Then try blowing on it.
At first, all you've got are normal bubbles -- and some of them break right away. But some bubbles will live long enough to freeze! Their perfect surfaces develop wrinkles and then they break. But the fragments of frozen bubbles -- unlike normal bubbles -- don't disappear. Pieces of frozen soap film, which looks like broken eggshells, fall to the ground.
Behind the Scenes
A bubble's skin is like a sandwich: there is a layer of water molecules between two layers of soap molecules. Temperatures of 10 F and below are well below the freezing point of water (32 F), which is cold enough to ensure that the thin layer of water in the bubble will freeze quickly before the bubble has the chance to burst.
The bubbles formed by drawing a wand through the air freeze almost instantly. The bubbles blown by mouth contain warm air. When they hit the cold outside air, the air inside the bubble contracts as it cools, causing the skin to crinkle like plastic wrap. The soap film adds strength to the frozen wall of the bubble. When an unfrozen bubble bursts, the liquid soap film forms tiny drops as soon as the air escapes. The soap film in a frozen bubble is solid and it stays that way even if it's broken into pieces.
I've got another great cold weather activity next week. See -- there are advantages to living in northern climates at this time of year!
Article By Vicki Cobb
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